Studies on the influence of gonadotrophin levels in the early follicular phase on the ovarian response to stimulation.

The gonadotrophic regulation of folliculogenesis has been extensively investigated but little attention has been paid to the influence of early follicular phase levels of endogenous FSH and the FSH/LH ratio when planning ovulation stimulation therapy for IVF. The influence of these factors was investigated in the three studies reported in this paper. A fixed schedule of ovulation stimulation therapy which employed standard treatment regimens, irrespective of the ovarian response, was used to eliminate variation due to treatment factors. Cycles were pretreated with an oestrogen-progestogen contraceptive pill or a progestogen (norethisterone). It was found that both oestrogen-progestogen and progestogen alone decreased the plasma FSH level, although the FSH/LH ratio was significantly reduced only by oestrogen-progestogens. In clinical IVF studies, oestrogen-progestogen pretreatment was associated with a significant reduction in the preovulatory concentration of oestradiol in plasma and the number of aspirated follicles, compared to norethisterone. The administration of FSH for 2 days following oestrogen-progestogen pretreatment and prior to the fixed schedule of ovulation stimulation normalized ovarian steroidogenesis and follicular development. Early follicular phase supplementation with FSH had no influence on progestogen pretreated cycles. The final experiment investigated the influence of FSH/LH levels in the early follicular phase on the outcome of ovarian stimulation. The preovulatory oestradiol concentration was reduced when baseline FSH/LH levels were low compared with when these values were high. Administration of FSH for 2 days in the early follicular phase improved the preovulatory level of oestradiol when baseline FSH/LH was low but had no effect when baseline FSH/LH levels were high.(ABSTRACT TRUNCATED AT 250 WORDS)